(d) : The chief water conducting elements of xylem in gymnosperms are tracheids. These are elongated cells with tapering ends and are dead because of deposition of lignin. These show scalariform, annular, reticulate or bordered pitted thickening. These are the only water conducting xylem elements in both gymnosperm and pteridophytes. Generally vessels are absent in gymnosperm with exceptions like Gnetum, Welwitschia, Ephedra.